将dropdownbox的IEnumerable转换为selectlistItem

Question

我有这个方法可以生成3个日期。我希望能够在下拉列表中使用日期。我需要它返回一个selectlistItem。我如何转换它？

        public static IEnumerable<MyDates> GenerateLastThreeDates()
        {
            IEnumerable<MyDates> rangeList = new[] { 1, 2, 3, 4 }.Select(n => DateTime.Now.Subtract(TimeSpan.FromDays(n))) // Transforming the integer (kind of index of days) array into dates.
                .Where(n => n.DayOfWeek != DayOfWeek.Sunday).Take(3) // Removing the Sunday and taking 3 days only.
                .Select(n => new MyDates() { Dateseries = n }); // Converting the date in your MyDates structure.
            return rangeList.ToList();
        }

我试过了，但是没有成功。

        IEnumerable<SelectListItem> myCollection = GenerateLastThreeDates
                                           .Select(i => new SelectListItem()
                                                        {
                                                            Text = i.ToString(), 
                                                            Value = i
                                                        });


        public class MyDates
        {
            public DateTime Dateseries { get; set; }
        }

Answer 1

将controller

• Convert instances

• Store data中的日期生成到SelectListItem ViewData中的列表中-这就是如何使用ViewData:

将非模型(即单向数据，而不是双向数据)传递到列表中的视图

例如：

控制器

public class FooController : Controller
{
    private static IEnumerable<SelectListItem> GenerateLastThreeDates()
    {
        // note that your code should be timezone-aware, so consider using DateTimeOffset instead of DateTime
        // also, never reference DateTime.Today (or Now, or UtcNow) in a loop - because the value can change in successive calls, instead you should store the value and re-use the cached copy
        DateTime now = DateTime.Today; 
        return Enumerable.Range( 1, 4 )
            .Select( n => now.AddDays( -n ) )
            .Where( d => d.DayOfWeek != DayOfWeek.Sunday )
            .Take( 3 )
            .Select( d => new SelectListItem()
            {
                Value = d.ToString("o"), // "o" for the RoundTrip format
                Text = d.ToString("d")
            } );
    }

    [HttpGet]
    public ActionResult Index()
    {
        this.ViewData["dates"] = GenerateLastThreeDates();
        return this.View( new IndexViewModel() );
    }

    [HttpPost]
    public ActionResult Index(IndexViewModel viewModel)
    {
        if( this.ModelState.IsValid )
        {
            DoSomething( viewModel.SelectedDate );

            return this.RedirectToAction( nameof(this.Index) );
        }
        else
        {
            this.ViewData["dates"] = GenerateLastThreeDates();
            return this.View( viewModel );
        }
    }

}

ViewModel.cs

public class IndexViewModel {

    [Required]
    public DateTime SelectedDate { get; set; }
}

View.cshtml

@{ IEnumerable<SelectListItem> dates = (IEnumerable<SelectListItem>)this.ViewData["dates"]; }

<p>Select a date: @Html.DropDownListFor( m = m.SelectedDate, dates )</p>

Answer 2

您的GenerateLastThreeDates方法返回一个MyDates集合，该集合中的每个项都有一个Dateseries属性，您将为该属性设置日期和时间。因此，在执行select方法调用时，基本上需要选择该属性。

var myCollection = GenerateLastThreeDates()
                     .Select(i => new SelectListItem
                                      {
                                        Text = i.Dateseries.ToString(), 
                                        Value = i.Dateseries.ToString()
                                      });

myCollection是SelectListItem的集合，其中的Text和value属性保存日期值的测试版本。您可以使用此类通过Html.DropDownListFor或Html.DropDownList辅助方法来构建select元素。

Answer 3

我通常只像这样定义扩展方法：

    public static List<SelectListItem> ToSelectListItems<T>(this IEnumerable<T> collection, Func<T, object> textSelector, Func<T, object> valueSelector, string emptyText = "- Choose-",
        string emptyValue = null)
    {
        var result = new List<SelectListItem>();

        if (collection != null)
        {
            var items = collection
                .Select(x => new SelectListItem
                {
                    Text = textSelector(x)?.ToString(),
                    Value = valueSelector(x)?.ToString()
                })
                .ToList();
            result.AddRange(items);
        }

        if (emptyText != null)
        {
            result.Insert(0, new SelectListItem { Text = emptyText, Value = emptyValue ?? string.Empty });
        }
        return result;
    }

然后：

1)将可能的值作为任意IEnumerable<T>添加到模型中

public class MyModel
{
    public int CountryId { get; set; }
    public List<Country> AllCountries { get; set; } = new List<Country>();
}

2)在控制器操作中填充可能的值：

public ActionResult Index()
{
    var model = new MyModel
    {
        AllCountries = _repository.GetCountries();
    };

    return View(model);
}

3)直接在视图中使用该扩展方法：

@Html.DropDownListFor(x => x.CountryId, Model.AllCountries.ToSelectListItems(x => x.CountryName, x => x.CountryId))